This is an open access article under the CC BY license
(http://creativecommons.org/licenses/by/3.0/).

Sponsor:

This research has been kindly supported by the Austrian Science Fund through the project “KnowLand—Knowledge and Semantics in Landform Classification” (FWF-P23818-N23), and through the “Doctoral College GIScience” (FWF-DK1237-N23).